1. Field of the Invention
The present invention pertains to the preparation of fluorinated propanes and tri- and tetra-fluorinated propenes. More particularly, the invention concerns a process for the production of the fluorinated propenes CF.sub.3 CH.dbd.CH.sub.2 and CF.sub.3 CH.dbd.CHF, and the fluorinated propane, tetrafluoropropane CF.sub.3 CH.sub.2 CH.sub.2 F.
2. Description of the Prior Art
Fluorinated propenes such as trifluoropropene (CF.sub.3 CH.dbd.CH.sub.2) are useful monomers for the manufacture of fluorosilicones and in the production of fluorinated chemical intermediates such as trifluoropropene epoxide and 3,3,3-trifluoropropylbenzene. Tetrafluoropropene finds use as a copolymer with ethylene, see U.S. Pat. No. 3,472,826 and Chem. Abstr., 71 (1969) 125454y). Tetrafluoropropane (HFC-254fb, CF.sub.3 CH.sub.2 CH.sub.2 F) is known as a blowing agent (Chem. Abstr. 114 (1991) P83236c) and heat transfer agent (Chem. Abstr. 114 (1991) P125031q).
Trifluoropropene has been made by two known prior art processes. In both processes the first step is the addition of CCl.sub.4 to ethylene to produce CCl.sub.3 CH.sub.2 CH.sub.2 Cl. Fluorination of the latter using a liquid phase fluorination process, such as HF in conjunction with an antimony catalyst, provides CF.sub.3 CH.sub.2 CH.sub.2 Cl which is subsequently dehydrochlorinated to give CF.sub.3 CH.dbd.CH.sub.2 (see A. L. Henne, et al, J. Am. Chem. Soc., 72 (1950) 3369). Alternatively, the fluorination of CCl.sub.3 CH.sub.2 CH.sub.2 Cl in a vapor phase process gives CF.sub.3 CH.dbd.CH.sub.2 directly (See German Patent 1 140 928).
Tetrafluoropropene has been made by the dehydroiodination of CF.sub.3 CH.sub.2 CHFI with alcoholic KOH (R. N. Hazeldine, et al, J. Chem. Soc., (1953) 1199), by the dehydrofluorination of CF.sub.3 CH.sub.2 CHF.sub.2 with KOH (I. L. Knunyants, et al, Izvest, Akad. Nauk S. S. S. R. Otdel. Khim. Nauk., (1960) 1412; Chem. Abstr. 55:349f), and by the addition of HF to trifluoropropyne (R. N. Hazeldine, et al, J. Chem. Soc., (1952) 3483).
Tetrafluoropropane, CF.sub.3 CH.sub.2 CH.sub.2 F, has been made by the reaction of ClF with CCl.sub.3 CH.sub.2 CH.sub.2 Cl (N. N. Chuvatkin, et al, Zh. Org. Khim., 18 (1982) 946; Chem. Abstr., 97: 144272r), by the fluorination of CF.sub.3 CH.sub.2 CH.sub.2 I with HgF, and via Zn reduction of CF.sub.3 CH.sub.2 CHFI (R. N. Hazeldine, et al, J. Chem. Soc., (1953) 1199) or CF.sub.3 CH.sub.2 CHFBr (P. Tarrant, et al, J. Am. Chem. Soc., 77 (1955) 2783).
The above processes suffer from several drawbacks. These include the use of expensive starting materials or reagents, such as CF.sub.3 I or HgF, or hazardous reactants such as ClF. Where dehydrohalogenations are required, a significant amount of waste is produced. For example, in the dehydrofluorination of CF.sub.3 CH.sub.2 CHF.sub.2 with KOH, an organic solvent is generally used, and an excess of KOH is generally employed in order to maintain a concentration of base which results in a high organic conversion. This produces a waste mixture of KOH and KF. While the prior art process for CF.sub.3 CH.dbd.CH.sub.2 appears attractive from the above considerations, it is not readily apparent how it might be used as a suitable raw material for CF.sub.3 CH.dbd.CHF. The use of CF.sub.3 CH.dbd.CH.sub.2 as a raw material for CF.sub.3 CH.sub.2 CH.sub.2 F via HF addition, is not without drawbacks since dimerization may compete with HF addition (see for example, M. Van Der Puy, et al, J. Fluorine Chem., 76 (1996) 49).
Dehydrofluorination of certain hydrofluorocarbons is known. For example, HCF.sub.2 CH.sub.2 F was dehydrofluorinated over a fluorinated alumina catalyst at about 425.degree. C. and gave mainly CHF.dbd.CHF (See U.S. Pat. No. 3,432,562 (1969)). 1,1,1-Trifluoroethane was dehydrofluorinated at 400.degree. C. using NiO, Fe.sub.2 O.sub.3 or ZnO as the catalyst (See F. H. Walker, et al, J. Org. Chem., 30 (1965) 3284). Conversions were 30 to 63%. Thermal, non-catalytic dehydrofluorinations require substantially higher temperatures. For example, CH.sub.3 CF.sub.2 CH.sub.3 was dehydrofluorinated to CH.sub.3 CF.dbd.CH.sub.2 at 731.degree. C. with a conversion of only 42% (See P. R. Austin, et al, J. Am. Chem. Soc., 75 ((1953) 4834). All of the foregoing disclosures are incorporated herein by reference. It is an object of this invention to overcome the above limitations via a process which is low cost, both from a standpoint of raw material cost and capital cost, which is amenable to scale, and which produces little waste. It is therefore a further objective to provide a process for producing trifluoropropene, tetrafluoropropene and tetrafluoropropane at low cost by utilizing the same or similar process equipment for each reaction step.